examples/tests/mpu_walk_region: handle missing button driver
examples/tests/mpu_walk_region: handle missing button driver

Signed-off-by: Leon Schuermann <be92910ae7bb6f58bb9b7c6f845bc30640119592@is.currently.online>

tock/libtock-c,tock/libtock-c,tock/libtock-c